The fresh snow arrived as predicted with heavy chutes today over the Northern Alps and at altitude in the Western Pyrenees. These have been accompanied by some strong winds and the existing snow pack is frequently unstable. Backcountry travellers should take care over the coming days, particularly on Sunday where fresh snowfall is expected.
Laurent Feuillatre weather forecaster with Météo France at Chamonix was certainly breather a sigh of relief. “We have been forecasting snow for ten days, but because it falls straight at the start of the season no-one believes us, they say we have been taking back handers from the Tourist Office”. The forecasters are predicting another big fall mid-week with cold weather through until early January.
There was a return to colder, unstable conditions with a strong wind from the South-East, gusting to 80km/h at times. Around 10 to 20cm of fresh snow fell during the course of Thursday night and a further 30 cm is expected today above 1200 meters. Winds should drop over the weekend and swing around to the North with perhaps a further 50cm of snow on Sunday. All this is good news for the ski resorts but off-piste and backcountry travellers should take great care. In many sectors, particularly below 2000 meters and higher on southern aspects there is no base, attention should be paid obstacles (rocks, barbed wire etc) hidden by the fresh snow.
The existing snowpack where present, dates to the start of December and has been worked by the sun and wind. Faceted crystals are present at altitude on east-south-west sectors and the snow is hard on northern aspects. The fresh snow will bond poorly to the existing base. The strong southerly winds Thursday and Friday will move a lot of snow onto north facing slopes. With the continuing snowfall on Sunday there is the possibility of spontaneous avalanches where the snow pack is overloaded. Otherwise the quantity of fresh snow will lead to soft slab formation over northern aspects with a localised risk on southern aspects. These slabs could be triggered by the passage of a single person.
Southern]http://pistehors.com/backcountry/wiki/Ski-Areas/Southern-Alps]Southern Alps[/url]
The weather system from the north-west has had trouble penetrating into the Southern Alps and has brought just 10cm of fresh snow in the north of the sector. A further 10cm is expected on Sunday. The weather should be fairly good on Saturday but with a strong wind (100-120km/h at 3000 m) at altitude and freshening temperatures.
The snow cover is poor for the season; it is only possible to ski to 2400/3000 meters except in some sheltered north facing bowls. The snow pack is relatively stable having undergone a number of freeze-thaw cycles over the fortnight except on Northern aspects where depth hoar may have formed with colder temperatures above 2,300 meters with a loss of cohesion of this layer.
The old snow has little cohesion on northern aspects and has a sun or wind crust on southern aspects. The fresh snow over the course of the next few days will not greatly change the stability of the snow pack. However the strong north-west to north wind will have transported some snow onto lee slopes (generally south-east facing) forming new slabs on a stable snow pack. There is a small risk that a backcountry traveler could trigger an avalanche especially with the fresh snow on Sunday.
Up to 10cm of fresh snow is expected above 1500 meters in the western mountains accompanied by a very strong easterly wind with gusts to 130km/h dropping to 80km/h on tomorrow. The fresh snow has fallen on surface hoar or frozen snow. With the strong wind there are slabs on west slopes and fresh cornices and slabs will form on south and east slopes. The snow pack is only moderately stabilised and sensitive to the passage of even single skiers, snowboarders or snowshoers.
Moderate to strong snowfall is expected tonight and tomorrow moving in from the west with the snow/rain limit situation around 2200 meters dropping to 1600 meters overnight. There may be up to 50cm of fresh snow above 2500 meters accompanied by a strong north-west wind blowing at 80-100km/h at altitude. The snow cover is good towards the east and above 2000 meters in the west but the ridgelines have been stripped of snow by the recent strong winds. It is possible to ski to 1600 meters on northern slopes. Last week’s fresh snowfall in the east has largely stabilized.
The rainfall may lead to some wet snow avalanches but the subsequent colder temperatures should stabilize northern slopes below 2200 meters. The strong wind will form fresh slabs at altitude. On north-west to north-east these will sit on faceted snow with little cohesion. An avalanche could be triggered by the passage of a single skier.
References
Météo France issues daily avalanche bulletins for the French Alps, Corsica and Andorra. You should ideally consult at least the previous 5 days bulletins prior to your trip.
Henry’s Avalanche Talk publishes a daily translation of the Météo France bulletin for the Savoie area.